Modem computer systems rely on data modems and standard telephone services for remote transfer of digital information. Modems are used in several applications, such as bulletin board services (BBSs), computers, and computer networks. Modems are also used for automated banking and credit card transactions.
FIG. 1 shows a prior art modem installation 150 wherein a modem 110 is collocated with a computer system 100 and connected to a telephone service 130 via telephone cable 120. Modem 110 may be located internally or externally to computer system 100. Connection 140 is through the backplane of computer system 100 if modem 110 is internally connected and connection 140 is a cable if modem 110 is externally connected. Computer system 100 may be a personal computer, a network of computers, mainframe, or other specialized computing hardware.
Telephone services offer encrypted caller identification information ("caller ID" information) to users for identification of the calling party. This information includes the caller's name, telephone number, and address. However, the signaling protocol used to transmit the caller ID information varies from country to country. In the United States, the caller identification information is transmitted after the first ring in an incoming telephone call. In the United Kingdom, the caller identification information is transmitted before the first ring and the transmission of the data is signaled by a line reversal of the tip and ring telephone lines. This is accomplished by swapping the signals on the tip and ring lines. Therefore, caller ID interfaces designed to detect caller ID information after a first ring will not function on services which use the line reversal as a signaling method.
There is a need in the art for a caller ID interface having line reversal detection. The caller ID interface should be designed to distinguish line reversals over other transient noise and ringing signals. Furthermore, the caller ID interface must not confuse other signaling tones with the line reversal.